1. Field of the Invention
The present invention relates to a mask for crystallizing a semiconductor layer and a method of crystallizing semiconductor layer using the mask. More particularly, the present invention relates to a mask for crystallizing a semiconductor layer used for crystallizing amorphous silicon into polycrystalline silicon, and a method of crystallizing semiconductor layer using the mask.
2. Description of the Related Art
Generally, liquid crystal display (LCD) devices employ amorphous silicon thin-film transistors (a-Si TFTs). When a high-resolution display quality is needed, LCD devices may employ polycrystalline silicon thin-film transistors (poly-Si TFTs). The poly-Si TFTs are mainly employed in organic light-emitting display devices having organic light-emitting diodes (OLED) driven by current.
In order to form polycrystalline silicon (poly-Si) thin film in a poly-Si TFT, the polycrystalline silicon thin film is formed directly on a substrate. Alternatively, an amorphous silicon thin film is first formed on a substrate, and then the amorphous silicon thin film is heated using a laser beam to form the polycrystalline silicon thin film.
In the laser beam heat processing method, the amorphous silicon thin film is melted into a liquid state when the laser beam irradiates the substrate. The melted silicon is grown, centered on a crystal nucleus, to be rearranged into a plurality of grain shapes having superior crystalline properties. The amorphous silicon thin film is thereby converted into a polycrystalline silicon thin film having higher electrical mobility than the amorphous silicon thin film.
Although the laser beam may directly irradiate the substrate; the laser beam may irradiate the substrate through a mask. Here, the mask may include a plurality of slit portions arranged in two rows to transmit the laser beam.
As the substrate is moved with respect to the mask, the laser beam is transmitted through the mask to intermittently irradiate the substrate. Here, the laser beam-transmitting slit portions induces a side growth of amorphous silicon of the substrate, so that the amorphous silicon is crystallized into polycrystalline silicon. One method of crystallizing the amorphous silicon into polycrystalline silicon is sequential lateral solidification (SLS), which uses a technique of excimer laser annealing.
However, this method of crystallizing the amorphous silicon into polycrystalline silicon by the SLS technology forms a boundary surface between the polycrystalline silicon or a protrusion in the direction of the substrate's movement. When the boundary or the protrusion is formed along the direction of the substrate's movement, electrical characteristics of the poly-Si TFT may be decreased due to the boundary surface or protrusion.